This application claims the priority benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2005-331859 filed on Nov. 16, 2005, which is hereby incorporated in its entirety by reference.
1. Field
The disclosed subject matter relates to a semiconductor light-emitting device and a surface light source using the same. In particular, the disclosed subject matter relates to a semiconductor light-emitting device and a surface light source for use in backlights for liquid crystal displays, panel illumination devices, general purpose illumination devices, and the like.
2. Description of Conventional Art
Currently, semiconductor light-emitting devices have been utilized in a variety of fields and in different ways. In one exemplary use, a semiconductor light-emitting device is combined with a light guide plate to form a surface light source. Such a surface light source can be incorporated into a backlight for a liquid crystal display, a panel illumination device, a general purpose illumination device, and the like to serve as a planar illumination light source.
FIG. 1 shows a conventional semiconductor light-emitting device 54 as one example. This type of semiconductor light-emitting device 54 can be fabricated as follows: First, a molded package body 51 is produced by insert-molding a pair of lead electrodes 50 using a resin material. In the molded package body 51, a recessed portion having an opening is formed. End portions of the separated lead electrodes 50 are exposed on the inner bottom surface of the recessed portion so as to be opposed to each other. Other end portions protrude from respective widthwise side walls of the molded package body 51 and are bent so as to follow the respective widthwise side walls and to extend along a lengthwise side wall. A semiconductor light-emitting element 52 is placed on one of the lead electrodes 50 exposed on the inner surface of the recessed portion. The semiconductor light-emitting element 52 has a pair of electrodes formed on the upper side thereof, and these electrodes are connected through respective bonding wires 53 to the respective lead electrodes 50 exposed on the inner bottom surface of the recessed portion. In addition, a transparent sealing resin is filled into the recessed portion to seal the semiconductor light-emitting element 52 and the bonding wires 53 with the resin. The thus prepared semiconductor light-emitting device 54 of this type is referred to as a side-view type (side surface light-emission type) semiconductor light-emitting device (see, for example, the conventional art reference to Ishida Masashi: Japanese Patent Laid-Open Publication No. 2004-193537).
A surface light source can be formed by combining the semiconductor light-emitting device having the aforementioned structure with a light guide plate. A general configuration thereof is illustrated in FIG. 2. First, a circuit substrate 55 is prepared, on which circuit components for driving the semiconductor light-emitting device 54 are mounted. Then, the semiconductor light-emitting device 54 is placed on the circuit substrate 55 such that the light emission direction thereof is parallel to the surface of the circuit substrate 55. The bent lead electrodes 50, which extend along the lengthwise side wall of the semiconductor light-emitting device 54, are connected to a circuit pattern formed on the circuit substrate 55 through respective conductive members. The semiconductor light-emitting device 54 and a light guide plate 57 are arranged at an appropriate distance therebetween such that a light emission surface (opening surface) 56 of the semiconductor light-emitting device 54 (united with the substrate 55) is opposed to a side surface serving as a light incident surface 58 of the light guide plate 57.
A conventional example of a conventional semiconductor light-emitting device 69 is shown in FIG. 3. In the semiconductor light-emitting device 69, a pair of thin metal plates 60a and 60b are bent to have a generally square U-shaped cross section, and are arranged at a predetermined distance therebetween so as to be opposed to each other. Each of the thin metal plates 60a and 60b serves as an electrode for introducing electric power from an external drive source. A bowl-like recessed portion 61 having an opening is provided in the thin metal plate 60a. A semiconductor light-emitting element 63 is placed on an inner bottom surface 62 of the recessed portion 61 through a conductive adhesive 64 to provide electrical continuity between a lower electrode of the semiconductor light-emitting element 63 and the thin metal plate 60a. Meanwhile, an upper electrode of the semiconductor light-emitting element 63 is connected to the thin metal plate 60b through a bonding wire 65 to provide electrical continuity between the upper electrode of the semiconductor light-emitting element 63 and the thin metal plate 60b. A first resin 66 is filled into the recessed portion 61 to seal the semiconductor light-emitting element 63 and the bonding wire 65 with the resin. In addition to this, a second resin 67 forms a condensing lens portion 68 and simultaneously covers the sealed portion. This type of semiconductor light-emitting device 69 is referred to as a top-view type (front surface light-emission type) semiconductor light-emitting device (see, for example, the conventional art reference to Akira Koike: Japanese Patent Laid-Open Publication No. 2002-314148).
A description will now be provided regarding a general method for constituting a surface light source by combining the semiconductor light-emitting device having the aforementioned structure with a light guide plate. For example, as shown in FIG. 4, the thin metal plates 60a and 60b, which have been bent inside the lower portion of the semiconductor light-emitting device 69, are mounted on and connected through respective conductive members to a circuit pattern 71 formed on a metal base 70. The semiconductor light-emitting device 69 and a light guide plate 72 are arranged at a predetermined distance therebetween such that a light emission surface (the condensing lens portion 68) of the semiconductor light-emitting device 69 is opposed to a side surface serving as a light incident surface 73 of the light guide plate 72. Furthermore, a heat dissipating member 74 such as a heat dissipating plate or a heat sink is disposed on the bottom surface of the metal base 70. On the rear side of the metal base 70, a circuit substrate 75 is disposed on which circuit components for driving and controlling the semiconductor light-emitting device 69 are mounted.
In this case, the semiconductor light-emitting device may not be directly mounted on the metal base. In contrast to the abovementioned case, first, the semiconductor light-emitting device may be mounted on and connected through a conductive member to a semiconductor light-emitting device-mounting substrate on which a circuit pattern is formed, and this substrate may be attached to the metal base.
It should be appreciated that the shape of the metal base is not limited to a triangular prism as shown in FIG. 4, but different shapes such as a square prism, a flat plate, and an angle may be employed. The metal base is designed to have an optimal shape in view of various conditions such as a placement space and heat dissipation effect.
Meanwhile, a semiconductor light-emitting element typically becomes hot when the element is turned on (driven), and the element typically has a reduced light emission efficiency due to the heat generated. Therefore, one consideration in the manufacture of a semiconductor light-emitting device is the suppression of temperature increase which can be accomplished by dissipating heat generated when a semiconductor light-emitting element is turned on to thereby suppress the reduction in the light emission efficiency. In this case, due to the structure of the semiconductor light-emitting device, the heat generated by the semiconductor light-emitting element is dissipated outside the semiconductor light-emitting device through a radiator connected to a heat-conducting body on which the semiconductor light-emitting element is placed. Therefore, the heat-conducting body greatly contributes, directly or indirectly, to the suppression of temperature increase of the semiconductor light-emitting element. In other words, factors for suppressing the temperature rise include good heat conductivity of the heat-conducting body on which the semiconductor light-emitting element is placed.
In the semiconductor light-emitting device of the abovementioned side-view type, the semiconductor light-emitting element is disposed on the lead electrode. In this lead electrode, the distance between the placement position of the semiconductor light-emitting element and a connection position on the circuit pattern of the circuit substrate on which the semiconductor light-emitting device is mounted is large. Therefore, the heat resistance of the lead electrode between the placement position and the connection position becomes high, and thus heat conductivity is poor.
Furthermore, when a surface light source is constituted by combining the semiconductor light-emitting device with a light guide plate, the thickness of the entire surface light source is relatively large since the semiconductor light-emitting device is mounted on the circuit substrate as shown in FIG. 2. Thus, it is difficult to reduce the thickness of backlights for liquid crystal displays, panel illumination devices, general purpose illumination devices, and the like into which the surface light source is incorporated.
On the other hand, in the semiconductor light-emitting device of the top-view type (see, for example, FIGS. 3 and 4), the semiconductor light-emitting element is mounted on the thin metal plate. In this case, a portion of the thin metal plate immediately below the position on which the semiconductor light-emitting element is disposed, is directly in contact with the metal base. Thus, the heat resistance between the semiconductor light-emitting element and the metal base serving as a radiator is low, and thus heat conductivity is good.
However, in this case, an insulating layer and the circuit pattern are typically formed on the metal base in order to mount the semiconductor light-emitting device thereon and connect it thereto, and thus a complicated and high cost manufacturing step must be provided. Moreover, when a backlight for a liquid crystal display, a panel illumination device, a general purpose illumination device, or the like is constituted, the number of components increases since a heat radiation member such as the metal base is provided, and therefore, the structure becomes complicated. This may restrict design flexibility and cause an increase in manufacturing cost.